An ultrasonic emitter can be used to determine the location of items that contain ultrasonic receivers, such as a mobile communication device present within a retail, factory, or warehouse environment, for example. The ultrasonic emitter can transmit ultrasonic energy in a short burst which can be received by an ultrasonic transducer (microphone) in the ultrasonic receiver, thereby establishing the presence of the device within the environment.
Further, the use of several ultrasonic emitters distributed within the environment can also be used to provide a specific location of a particular device using techniques known in the art such as triangulation, trilateration, and the like. However, unlike radio frequency locationing systems, ultrasonic locationing systems suffer from particular problems related to the characteristics of ultrasonic sound waves and their environment of use. For example, ultrasonic signals are easily subject to noise. In particular, broadband noise events (which are typical of impact noise) can fall within the frequency band of interest, and cannot be filtered out without also filtering the desired signal. As a result, accurately triggering a location measurement using an incoming pulse in a flight time based locationing system can be difficult for amplitude based detectors if there are a lot of in-band noise events that could result in false triggers. A pulse design is needed such that additional metrics can be used in order to accurately identify it as a valid pulse.
Ultrasonic ranging pulses typically have very short durations to prevent reflections from arriving at the receiver before the direct signal is completely received. However, a very short burst of an ultrasonic signal implies little information can be added to the burst. Further, increasing the “signature” of a pulse is difficult when pulses are required to be short in duration which is the case for typical locationing systems. In addition, detectors of single pulses are very susceptible to impact noise or noise tones greater in length than the pulse period. Moreover, the selectivity of a very short Fast Fourier Transform (FFT) or a Goertzel algorithm run on a single pulse can be poor, i.e. the system is susceptible to tones at nearby frequencies.
Accordingly, there is a need for an improved technique to resolve the above issues with an ultrasonic locationing system. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing background.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.